Message-ID: <4E4C2FEB.5060301@2ndQuadrant.com>
Date: Wed, 17 Aug 2011 17:17:31 -0400
From: Greg Smith <greg@2ndQuadrant.com>
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To: pgsql-performance@postgresql.org
Subject: Re: Raid 5 vs Raid 10 Benchmarks Using bonnie++
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On 08/17/2011 02:26 PM, Ogden wrote:
> I am using bonnie++ to benchmark our current Postgres system (on RAID 
> 5) with the new one we have, which I have configured with RAID 10. The 
> drives are the same (SAS 15K). I tried the new system with ext3 and 
> then XFS but the results seem really outrageous as compared to the 
> current system, or am I reading things wrong?
>
> The benchmark results are here:
> http://malekkoheavyindustry.com/benchmark.html

Congratulations--you're now qualified to be a member of the "RAID5 
sucks" club.  You can find other members at 
http://www.miracleas.com/BAARF/BAARF2.html  Reasonable read speeds and 
just terrible write ones are expected if that's on your old hardware.  
Your new results are what I would expect from the hardware you've 
described.

The only thing that looks weird are your ext4 "Sequential Output - 
Block" results.  They should be between the ext3 and the XFS results, 
not far lower than either.  Normally this only comes from using a bad 
set of mount options.  With a battery-backed write cache, you'd want to 
use "nobarrier" for example; if you didn't do that, that can crush 
output rates.

-- 
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  www.2ndQuadrant.us